[MemoryLeak] Fix leak of FloatingRotationButton.mKeyButtonContainer from IRotationWatcher.Stub

Clear RotationButton and it's callbacks when RotationButtonController#onDestroy() is called.

Fix: 423710276
Flag: NONE - released code
Test: presubmit
Change-Id: I7b1199496bdcc0fa6281c1d193362b00367f848e